Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $57.36   5.350%   $60.4288   $60.43   $60.45   $60.40  
  Purchase #2 $24.72   4.258%   $25.7726   $25.77   $25.75   $25.80  
  Purchase #3 $125.87   11.145%   $139.8982   $139.90   $139.90   $139.90  
  Purchase #4 $27.42   5.485%   $28.924   $28.92   $28.90   $28.90  
  Purchase #5 $245.76   4.479%   $256.7676   $256.77   $256.75   $256.80  
  Purchase #6 $172.53   4.730%   $180.6907   $180.69   $180.70   $180.70  
  Purchase #7 $248.98   7.149%   $266.7796   $266.78   $266.80   $266.80  
  7 purchase totals = $902.64       $959.2615   $959.26   $959.25   $959.30